Local anesthetics are used in many dental procedures to prevent patient pain. Often, a topical anesthetic is applied to numb an area in preparation for the administration of a local anesthetic via injection. In some procedures, particularly those involving the maxillary teeth and the anterior mandibular teeth, local anesthetic is administered via buccal infiltration. During buccal infiltration, a needle is inserted into the soft tissue near the bone and the anesthetic is then injected through the needle so as to be in close proximity to the bone. The anesthetic then passes through pores in the outer cortical bone surface until it reaches nerve filaments inside the “spongy” cancellous bone.
Administration of anesthesia through infiltration is only effective where a sufficient amount of anesthesia is able to permeate through the surrounding tissues. For example, infiltration will fail where the local anesthetic is unable to diffuse through the cortical bone. Areas of the mouth where a thick cortical plate exists have limited ability to distribute and diffuse anesthesia into the cancellous bone where it can act on targeted nerves. Typically, the cortical plate is relatively thicker at mandibular teeth than maxillary teeth, and is relatively thicker at more posteriorly located teeth than more anteriorly located teeth. Thus, for some areas of the mouth such as near mandibular molars, infiltration is typically not a viable option for anesthetization.
A similar technique is intraligamentary injection, where the anesthetic is injected into the periodontal ligament(s) of the targeted tooth/teeth. The anesthetic then reaches the pulp via natural perforations in the tooth/teeth. This method, however, is often associated with sharp pain during injection as well as following the procedure. In addition, for posteriorly located teeth, it can be difficult to properly orient the syringe to a workable position for injecting the needle tip into the periodontal ligament.
In circumstances where infiltration and/or intraligamentary injection are not feasible, such as in various procedures involving mandibular molars, for example, a common anesthetization method is the inferior alveolar nerve block (“IANB”). An IANB is carried out by injecting the local anesthesia near the inferior alveolar nerve before it enters the mandibular foramen. Compared to anesthetization via infiltration, an IANB takes longer to take effect, and typically lasts much longer (e.g., on the order of an hour or several hours rather than minutes). Also, diffusion of the anesthesia effects the nearby lingual nerve, which innervates the tongue. After an IANB, a patient will lose sensation in their mandibular teeth (on one side of the mouth where the block was administered), the lower lip and chin, and parts of the tongue and lingual gingival tissue.
Although often effective for their purpose, IANBs have several limitations. In many circumstances an IANB is “overkill” because such a large portion of the mouth is anesthetized even though the actual targeted area needing it is small. Further, because of the time delay before numbing begins, it may be difficult for practitioners to accurately gauge the amount of anesthesia required. In addition, an IANB takes a relatively long time to wear off, and there is a risk of accidental self-inflicted trauma following the procedure. For example, a patient may unknowingly bite and injure the lip or tongue while tissues are still numb, or may inadvertently burn the mouth by drinking a fluid that is too hot.
Another technique is intraosseous administration of anesthesia. In this technique, the anesthesia is deposited directly into the cancellous alveolar bone near the root(s) of the targeted tooth to be anesthetized. To reach the spongy cancellous bone, a small hole must first be made in the outer cortical plate. Typically, this is accomplished using a drill (such as the commercially available “X-Tip” delivery system) or by using a relatively large gauge needle to puncture the cortical plate. Conventional methods of intraosseous delivery are limited by the difficulty of puncturing the cortical bone in certain areas of the mouth, such as near mandibular molars where the cortical plate is particularly thick. In addition, although a mechanical drill may alleviate some of the difficulties in puncturing the cortical bone, it can also cause the build up of heat which can damage surrounding tissues. Also, because the access hole must be made near the root(s) of the targeted tooth, there is an inherent risk that the drill will reach and damage the root(s).
In sum, nerve blocks such as an IANB are limited by their delayed onset, overly broad numbing effect, and overly long duration. More localized methods of anesthesia delivery can avoid some of these limitations, but are not always appropriate or available in particular circumstances and/or for particular teeth. Accordingly, there is a long felt and ongoing need for improved devices and methods for anesthetizing teeth and surrounding tissues.